I read a bunch of people suggestions with no success. however, i found the solution for my ps3!
'''symptoms''': 1) when unit first powered up it sounds like it's trying to elect disk. 2) disk can be inserted upon power up, but not any time after that.
'''problem''': the metal shield on the top of the disk drive was very slightly indented where the foam tape seals to the top lid. this was rubbing the internal plastic arms and not allowing them to return to the fully ejected state.
'''fix''': removed the metal shield, slightly bent outward, and reattached
'''now it works perfectly!'''